Save & Restart a Simulation

The SaveRestartProcess implemented in the Kratos Core enables the periodic saving of all data contained in the computing (MPM) model part. This functionality acts as a checkpoint system, allowing users to resume a simulation from the last saved state using the RestartUtility and without having to restart from the beginning.

Regularly saving data during a simulation is crucial for preventing data loss in case of unexpected interruptions. Additionally, it provides flexibility when the total simulation time is uncertain, allowing users to extend the simulation without losing progress.

Save Simulation Data: the SaveRestartProcess

Parameters & Defaults

{
    "kratos_module" : "KratosMultiphysics",
    "python_module" : "save_restart_process",
    "Parameters"    : {
        "model_part_name"              : "SPECIFY_MODEL_PART_NAME",
        "echo_level"                   : 0,
        "serializer_trace"             : "no_trace",
        "restart_save_frequency"       : 0.0,
        "restart_control_type"         : "time",
        "save_restart_files_in_folder" : true,
        "output_path"                  : "",
        "max_files_to_keep"            : -1
    }
}

model_part_name

String identifying the name of the MPM ModelPart (usually MPM_Material).

echo_level

An integer controlling the verbosity level of the simulation output. If greater than zero, messages are printed to the standard output.

serializer_trace

Serializer flag. Admissible values are:

• "no_trace" (default)
• "trace_error"
• "trace_all"

restart_control_type

Determines how the output is controlled and printed during the simulation. Acceptable values are:

• step: the restart file is generated at regular intervals, specified as a fixed number of time steps;
• time: the restart file is generated at regular intervals, specified in seconds.

restart_save_frequency

Selects the amount of output_control_type that needs to happend before printing a new restart file.

output_path

Specifies the name of the folder where the restart files have to be saved. If empty, the files are saved in a folder named model_part_name__restart_files.

save_restart_files_in_folder

If true, save restart files in folder specified by output_path, otherwise in the current path.

max_files_to_keep

Specifies the maximum number of restart files to keep. If set to -1, then keeps all the files (default).

Output Files Name

The name of the .rest files generated by the SaveRestartProcess is given by model_part_name + _ + a label indentifying the step or the time (depending on the restart_control_type setting) at which the file is written.

Therefore, the path of each file is one of the following:

• "save_restart_files_in_folder" : true

  → <current_path>/<output_path>/<model_part_name>_<step|time>.rest

• "save_restart_files_in_folder" : false

  → <current_path>/<model_part_name>_<step|time>.rest

Restart Simulation: the RestartUtility

For restarting a simulation using the .rest files generated by the SaveRestartProcess, the following parameters must be included in the solver_settings section of the ProjectParameters.json input file.

{
    "model_import_settings" : {
        "input_type"                      : "rest",
        "input_filename"                  : "",
        "input_output_path"               : "",
        "load_restart_files_from_folder"  : true,
        "restart_load_file_label"         : "1",
        "echo_level"                      : 0,
        "serializer_trace"                : "no_trace"
    }
}

input_type

Value must be "rest". Typically (i.e., when not using the restart) this field is set to "mdpa".

input_filename

String specifying the name, without the time/step label and the extension, of the rest files to be loaded. If the user has not changed the name of the files, this value must be set equal to the model_part_name (i.e., the value used by the SaveRestartProcess, see Output Files Name).

input_output_path

String specifying the name of the folder containing the rest files. If empty, the value is set to <input_filename>__restart_files.

save_restart_files_in_folder

If true, it is assumed that the rest files are contained in the folder specified by input_output_path.

restart_load_file_label

Label specifying the exact rest file to be loaded and used as starting point for the simulation, i.e., the number used as suffix in the rest files and denoting the time/step to which each file refers (see Output Files Name).

echo_level

An integer controlling the verbosity level of the simulation output. If greater than zero, messages are printed to the standard output.

serializer_trace

Serializer flag. Admissible values are:

• "no_trace" (default)
• "trace_error"
• "trace_all"

Source Code

kratos/python_scripts/save_restart_process.py

kratos/python_scripts/restart_utility.py